1. Technical Field:
This disclosure relates to gas turbine engines in general, and in particular, to an accessory drive for such engines.
2. Related Art:
Engines, such as jet turbine engines of a type used, for example, to propel commercial or military aircraft, require a number of engine accessories, such as electrical generators, oil and fuel pumps, hydraulic and coolant pumps and the like, in order to function. To operate these essential accessories, some of the power generated by the engine is taken off of the engine and coupled through an “accessory drive,” or “gearbox,” that is used to drive the accessories. The accessories, along with the gearbox, are typically coupled closely to the outer surface of the engine's housing, and within the engine's nacelle, if any, to minimize the space they occupy, e.g., for streamlining purposes.
Engines typically include one or more rotating shafts from which “secondary power” can be coupled to drive the engine's accessories through the gearbox. However, existing engine accessory gearboxes, which typically incorporate one or more trains of spur gears, entail a fixed relative speed between the engine and the accessories without the possibility of stopping or changing the relative speeds or loads of the accessories. This can result in gear backlash between the engine and the accessories when they are respectively sped up, slowed down, stopped, or operated intermittently, with concomitant shaft vibration and torsional resonance.